The present invention relates to a print head for a dot matrix printer having a plurality of print wires, and more particularly to a double print head in which a pair of print heads are disposed in the axial direction.
In order to increase the number of the print wires and to increase printing speed, a double print head is used. In the double print head, each print wire provided in a rear actuator is inevitably longer than that utilized in a front actuator. Accordingly, the moment of inertia of each moving element of the rear actuator becomes larger than that of the front actuator. Thus, the actions of the moving elements of the rear actuator are different from the actions in the elements in the front actuator. These differences which reduce the quality of the print. Namely, if materials of the print wires and armatures, the shapes of the armatures, and the diameters of the print wires and other elements of the front and rear actuators are the same. The impact force of the print wire of the front actuator, which has a short length, becomes larger than that of the rear actuator. Thus, uniform quality of the print cannot be obtained. Therefore, it is the object of the present invention to solve this technical problem thereby equalizing the actions of the print wires of both actuators.
In order to solve this problem, two methods are known. A first method is to change the electrical driving conditions in both actuators, and a second method is to change the materials of the print wires in both actuators (Japanese Patent Application Laid-open 59-95164).
However, such methods have produced further problems. The former method renders the driving circuit complicated. In the latter method, abrasion resistances of respective print wires are different from each other which makes the tone of the print irregular with time.